Method for preparation of aluminum-mercury alloys



United States Patent ()filice 3,318,692 Patented May 9, 1967 3,318,692METHOD FOR PREPARATION OF ALUMINUM- MERCURY ALLOYS Bernard Raclot,Paris, France, assignor to Societe Generale du Magnesium, Paris, FranceNo Drawing. Filed Apr. 7, 1966, Ser. No. 540,826 17 Claims. (Cl. 75-138)This application is a continuation-in part of my copending applicationSer. No. 328,195, filed Dec. 5, 1963, titled Aluminum Alloy, now PatentNo. 3,257,201, which application was a continuation-in-part of my thencopending application Ser. No. 852,961, filed Nov. 16, 1959, and titled,Aluminum Alloy, now abandoned.

This invention relates to an aluminum alloy formed of aluminum, mercuryand magnesium, with or with-out zinc, and it relates more particularlyto elements for use in electrolytic cells, such as anodes and the likeformed of such aluminum alloys.

It is known in the art that aluminum, which is in contact with mercuryor contains mercury, tends to oxidize in the open air very rapidly.Apparently, the mercury functions as a catalyst, greatly furthering theoxidation of aluminum, and, consequently, even extremely smallquantities of mercury are suflicient to cause this undesirable effect.

It is, therefore, universally admitted that in industrial applicationany contamination of aluminum with mercury must be strictly avoided.Where aluminum alloys with mercury are prepared, containing apredominant percentage of aluminum, .solid dispersions are obtainedhaving a very poor stability and oxidizing very rapidly when exposed toair or an oxygen-containing medium. The oxidation occurs so rapidly thata veritable mushrooming efiect of alumina can be observed. Inelectrolytic solutions such alloys are rapidly attacked and eventuallydestroyed by this highly undesirable oxidation. It is particularlydisadvantageous in electrolytic cells where the anode tends to decomposevery rapidly.

It is an object of the present invention ot provide an aluminum alloyhaving an improved resistance to corro- Sn. It is another object of thepresent invention to provide an aluminum alloy which can be easilypolished and is susceptible to furnish, when polished, a surface ofexceptionally high gloss and brilliancy.

It is a further object of the present invention to provide an aluminumalloy which can be more easily worked than the known aluminum alloys.

It is another object of the present invention to provide an aluminumalloy which can be most advantageously used for the production ofanodes, especially as used in electroytic cells, and it is a rela-tedobject to produce a new and improved anode of said alloy.

It is still another object of the invention to provide an anode,particularly for use in electrolytic cells composed of an aluminum alloyof the present invention, having a far greater efiiciency and a longerservice life as well as having a more slightly and evenly decreasingyield than electrolytic cells using anodes composed of conventionalalloys.

It is still a further object of the invention to provide an anode,particularly for use in electrolytic cells composed of an aluminum alloyof the present invention, which is particularly useful for the providingof objects with a protective layer by cathodic deposition, and whereinthe anode has a far greater elliciency while being consumed far lessrapidly and drastically than anodes composed of conventional alloys.

Further objects and advantages will become apparent upon reading thefollowing description of the invention.

The objectives of this invention are achieved by the preferred practiceof the invention by the formulation of an aluminum alloy containingmercury and magnesium as alloying elements with the magnesium present inan amount within the range of 0.5 to 15 percent by weight and preferablywithin the range of 3 to 8 percent by weight and with the mercurypresent in an amount within the range of 0.001 to 0.15 percent by weightand preferably in an amount within the range of 0.04 to 0.15 percent byweight, the remainder being aluminum plus small amounts of conventionalimpurities.

When Zinc is present as an alloying element in the combination withmercury and magnesium, it is preferred to limit the amount of zinc towithin the range of 0 to 4 percent by weight and preferably in :anamount within the range of 0.25 to 2.0 percent by weight. Thus thealuminum alloy of this invention may be defined as having the followingcomposition wherein the elements are given in percent by Weight:

There are a number of ways in which the materials can be formulated inpreparation of the aluminum alloy. By way of one example, the mercurycan be alloyed first with zinc or with a zinc alloy having as low amelting point as possible. The alloy is then melted with the necessaryamount of aluminum and magnesium to obtain the final composition.

According to a modification the alloy of mercury with zinc is preparedunder a pressure exceeding 1 atmosphere, preferably in the presence ofan inert gas such as argon. By following this procedure, thevolatilization of mercury is reduced to a minimum. Under theseconditions, the mercury is dissolved in the zinc to form master-alloycontaining from 5 to 20 percent of mercury. The master-alloy is thenalloyed with aluminum or an aluminum alloy in a quantity of, forexample, percent aluminum. I

In order to make operations at low temperature possible, the mercury ispreferably dissolved in the zinc/ aluminum eutectic having an aluminumcontent of 5 percent by weight and which melts at a temperature of 380C. This alloy is then diluted with the desired quantity of aluminum andmagnesium to make up the desired composition.

In accordance with another modification, preferably employed inthe'preparation' of .a master alloy containing mercury, thealuminum-zinc, the magnesium-zinc or tellurium-zinc components arereduced to a molten state. The mercury to be introduced is'housed in asyphon or tube that is sealed at one end and capped at the other endwith a cap that is formulated of the alloy materials or of an alloyformulated of one or more of the metals embodied in the alloy system butwhich has a melting point corresponding to the melting point of the meltand preferably lower. The capped end of the tube is plunged into themelt whereby, when the cap is heated by the adjacent materials to themolten state, the mercury flows from the tube directly into thesubmerged portion of the melt.

In the preferred practice in the preparation of the alloy of thisinvention, the mercury is formed first into a master alloy of zinc andmercury, which may be represented by the following compositions:

Percent by wt. Mercury 5 to 20 Zinc Balance Zinc 41.6 Magnesium 38.4Mercury 20.0

Mercury 15.0 Aluminum 3.9 Zinc 81.1

Mercury Tellurium Zinc 75 The latter ones find use in the preparation ofalloys containing little if any magnesium.

The necessary quantity of this alloy is then wrapped in several layersor otherwise enclosed with sheet of a metal of the desired alloy, suchas aluminum, magnesium, zinc, copper and the entire package is thenimmersed into a bath of molten aluminum whereby the mercury is releasedwhile within the bath greatly to minimize the amount of mercury thatmight be lost by vaporization.

The new alloy can be used for various purposes but particular advantageis found in making use of the alloy as anodes for electroyltic cells andparticularly for cathodic protection. When used in cathodic protection,due to the high value of potential of the alloys of this invention, theanodes promote the deposition of protective layers on the cathodes. Theknown anodes could not be used in a 'basic environment having a pH valueabove 10.8 and notably in the black liquor (aqueous solution of sodiumcarbonate, soda, and sodium sulphite). The anode consisting of the alloyof the invention can be safely used for these purposes. The same appliesto the application to certain brines in which the dissolved salts can'beprecipitated by permutating their respective metals with magnesium, ifan anode is used containing Mg as an adjuvant. The known anodes composedof an aluminum/zinc alloy cannot be used because of an excessivepolarization even at currents as low as milliamperes.

The anodes composed of the alloys of the invention have substantialnegative potential generally comprised between 1.1 and 2.0 voltsaccording to the environment in which they are used; the potentials areextremely stable over a long period of time. In addition they have anefficiency which is generally greater than 70 percent as compared withknown electrodes having an efficiency substantially below 70 percent,the efiiciency of conventional aluminum/zinc alloy electrodes notexceeding 50 percent.

The known aluminum/copper alloys for industrial use generally have acopper content of from 0.5 to 13 percent and particularly from 3 to 5percent. The alloys of the invention preferably contain copper in therange from 0.5 to 15 percent and more preferably yet from 1 to 5percent.

The excellent electro-chemical quality of the new alloys of theinvention makes it possible to prepare anodes for use in electrolytic orgalvanic or dry cells. The potential, the current density and the yieldof such electrolytic cells or dry cell batteries is greatly improved. Atthe same time the alloys of the invention are highly resistant tocorrosion and constitute an excellent anode for cathodic protection.

Most advantageously the aluminum alloys used for anodes in electrolyticcells, galvanic elements or dry cell batteries or cathodic protectioncontain both magnesium Example I An electrolytic cell is prepared havingan anode composed of an aluminum alloy containing 8.5 percent of Mg and0.125 percent of Hg, the rest being aluminum. The cathode is composed ofmanganese bioxide and carbon. The electrolyte consists of an aqueoussolution containing, for each liter of water:

NH Cl 250 Ammonium chromate 2 Lauryldimethylbenzylammonium 0.2 Sodiumbenzoate 5 The pH value of this solution is brought to 9.2 by addingammonia. The electromotive force of the cell is 1.85 volts.

Example 11 An electric cell is prepared having a cathode consisting of acarbon cylinder of .a diameter of 6 millimeters and a length of 65millimeters. The depolarizer consists of:

Percent M1102 Acetylene black 20 Barium chromate 5 The followingsolution is used for wetting the depolarizer: an aqueous solution havinga specific gravity of 28 Baum of calcium chloride containing per liter 1gram of barium chromate and 3 cubic centimeters of a 10% solution of thebromide of la-uryldimethylbenzylammonium.

The same solution, but with the addition of a jellifying substance, isused as the electrolyte.

The anode consists of an aluminum alloy containing 0.066 percent byweight of mercury, 6 percent of magnesium, the rest being aluminum. Theanode has an outer diameter of 33 millimeters and a length of 62millimeters, corresponding to the conventional dimensions of aconventional dry cell torch battery.

The electromotive force of the cell is 2.10 volts. The cell has aconstant yield of 250 milliamperes during 24 hours, i.e. 6 ah., untilthe voltage has been reduced to substantially half the initial voltage,i.e. 1.1 volts. Thereafter the discharge is continued for 12 hourswhereafter the voltage is 0.9 volt and the total capacity 9 ah.

In comparison a cell comprising a conventional zinc anode is tested inthe same manner. The discharge is continued for 16 hours, and theobtained capacity is thus 4 ah., the initial voltage being 1.5 volts andthe final voltage being 0.75 volt.

Thus, the alloy of the invention is greatly superior in that thedischarge up to percent of normal capacity furnishes 6 ampere hourscompared with only 4 ah. when using a conventional composition. Inaddition, the alloy of the invention is capable of furnishing a furtherappreciable amount of electricity in the order of 9 ampere hours afterthe voltage has dropped to 50 percent of the initial voltage which isnot possible with conventional compositions.

Instead of forming the anode in the previous example of the compositionset forth therein, the anode can be formed of an aluminum alloycontaining 0.06 percent by weight of mercury, 6.0 percent by weight ofmagnesium, 1.5 percent by weight of zinc, with the remainder aluminumplus impurities.

It will be understood that this invention is susceptible to furthermodification and, accordingly, it is desired to comprehend suchmodifications within this invention as may fall within the scope of theappended claims.

For instance, it is possible to introduce directly mercury, either inmolten aluminum or in a molten masteralloy containing all thecomponents, but no mercury, of the desired alloy, by means of the sealedtube described thereabove.

I claim:

1. In the method of producing an alumin um alloy containing mercury asan alloying element, the steps of reducing the aluminum containingcomponet to a molten state, wrapping a product of the group consistingof mercury and mercury alloys in a sheet of metal to form asubstantially enclosed package, submerging the package below the surfaceof the molten aluminum containing component whereby the product isheated while the wrapping of metal is melted away to release the heatedprod uct while submerged in the bath of molten component for alloyingwith said component without excessive loss of mercury vapors.

2. A method according to claim 1, in which the mercury alloy is an alloycontaining mercury and zinc.

3. A method according to claim 2, in which the mercury alloy is an alloycontaining mercury, zinc and mag nesium.

4. A method according to claim 2, in which the mercury alloy is an alloycontaining mercury, zinc and aluminum.

5. A method according to claim 2, in which the mercury alloy is an alloycontaining mercury, Zinc and tellurium.

6. A method according to claim 1, in which the metal of the sheet isaluminum.

7. A method according to claim 1, in which the metal of the sheet ismagnesium.

8. A method according to claim 1, in which the metal of the sheet iszinc.

9. A method according to claim 1, in Which the metal of the sheet iscopper.

It). A method according to claim 2, in which the master-alloy is analloy containing 5 to 20% by weight of mercury.

11. In the method according to claim 1, a process to produce the mercuryalloy by the steps of reducing to a molten state a component comprisingthe elements other than mercury of the alloy, introducing the mercuryinto an elongate tube which is tightly sealed at one end and sealed atthe other end with a cap of a meltable metallic material adapted to forma part of the alloy, plunging the tube downwardly into the bath ofmolten component whereby the temperature of the mercury within the tubeis raised and the cap is melted away to release the heated mercury intoa submerged portion of the molten bath of component whereby mercuryvapors are condensed and retained for alloying purposes with thecomponent.

12. The method as claimed in claim 11 in which the cap is formed of ametallic material having a melting joint below the temperature of themolten bath of com ponent.

13. The method as claimed in claim 11, in which the mercury isintroduced in an amount to supply the amount of mercury for the masteralloy with zinc.

14. The method as claimed in claim 11, in which the mercury isintroduced in an amount to supply the amount of mercury for the masteralloy with zinc and magnesium.

15. The method as claimed in claim 11, in which the mercury isintroduced in an amount to supply the amount of mercury for the masteralloy with zinc and aluminum.

16. The method as claimed in claim 11, in which the mercury isintroduced in an amount to supply the amount of mercury for the masteralloy with zinc and tellurium.

17. In the method of producing an aluminum alloy containing mercury asan alloying element, the steps of reducing the aluminum containingcomponent to a molten state, introducing the mercury into an elongatetube which is tightly sealed at one end and sealed at the other end witha cap of a meltable metallic material adapted to form a part of thealloy, plunging the tube downwardly into the bath of molten aluminumwhereby the temper ature of the mercury within the tube is raised andthe cap is melted away to release the heated mercury into a submergedportion of the molten bath of aluminum whereby mercury vapors arecondensed and retained for alloying purposes with the aluminum, themercury being introduced in an amount to supply the amount of mercurycalculated for direct alloying with the aluminum containing component.

References Cited by the Examiner UNITED STATES PATENTS 1,970,768 8/1934-Rabezzana et al 75-17O 2,087,269 7/1937 Stroup 75-138 2,758,082 8/1956Rohrman 75138 HYLAND BIZOT, Primary Examiner. DAVID L. RECK, Examiner.R. O. DEAN, Assistant Examiner.

1. IN THE METHOD OF PRODUCING AN ALUMINUM ALLOY CONTAINING MERCURY AS ANALLOYING ELEMENT, THE STEPS OF REDUCING THE ALUMINUM CONTAINING COMPONETTO A MOLTEN STATE, WRAPPING A PRODUCT OF THE GROUP CONSISTING OF MERCURYAND MERCURY ALLOYS IN A SHEET OF METAL TO FORM A SUBSTANTIALLY ENCLOSEDPACKAGE, SUBMERGIN THE PACKAGE BELOW THE SURFACE OF THE MOLTEN ALUMINUMCONTAINING COMPONENT WHEREBY THE PRODUCT IS HEATED WHILE THE WRAPPING OFMETAL IS MELTED AWAY TO RELEASE THE HEATED PRODUCT WHILE SUBMERGED INTHE BATH OF MOLEN COMPONENT FOR ALLOYING WITH SAID COMPONENT WITHOUTEXCESSIVE LOSS OF MERCURY VAPORS.